Don't use a template for nsswitch.conf

It will more than likely get into a never-ending fight with
authconfig. authconfig does not currently handle the sudoers line
though so append this if it is missing and then add or remove sss
(not ldap!) as necessary. Finally, the ldap_sudo attribute should be a
real boolean, not a string. Fixes #12.
Merge pull request #14 from yakara-ltd/no_nsswitch_template

Don't use a template for nsswitch.conf